This invention relates generally to chemically activated microporous membranes. More particularly, this invention relates to polyaldehyde activated microporous membranes and a process for making the same.
Aldehydes have been used in conjunction with a variety of materials, such as beads and microspheres. In addition, substrates including certain membranes have been chemically activated with aldehyde functional groups using methods such as oxidation.
Microporous membranes are also known. The traditional use of microporous membranes to filter materials has been based mainly on their physical properties, e.g., pore size, thickness, strength, etc. For example, retention by microfiltration membranes is accomplished mainly through mechanical sieving. Even in uses where the chemical properties of a membrane come into play, such as in gas separation or desalination, generally chemical bonding between the separated species and the membrane matrix is not employed.
A type of microporous membrane which is capable of reacting chemically with soluble or suspended species is the so-called "affinity membrane." Various affinity membranes are commercially available. Some, which are designed to interact specifically with only one or a few species in complicated mixtures, are improvements over traditional membranes which rely on physical separations. Examples of such highly specific interactions include antigen/antibody, hapten/antibody, apoprotein/cofactor and lectin/carbohydrate. Affinity membranes may be used in immunodiagnostic testing wherein the interaction between the antigen and antibody is particularly relevant.
But the currently available affinity membranes have certain drawbacks. For some, shelf life is limited because the active groups are destroyed by prolonged exposure to the atmosphere. For others, binding capacity is limited. Nonspecific binding, which can lead to false positive readings, is a problem as well. Nonspecific covalent binding is typically remedied by treating the membrane with a blocking agent. However, blocking agents do not always solve the problem satisfactorily.
There are also various shortcomings in the methods for making activated membranes. For example, some of the methods are limited to certain substrates or membrane polymers. An oxidation reaction, for example, is limited to membranes such as cellulose acetate, and would not activate other commercial membranes such as polysulfone, nylon or polypropylene. Also other chemical reactions may damage the pore structure of certain species of microporous membranes. In still others, clogging of the pores may present a problem.
The drawbacks and shortcomings mentioned above illustrate some of the unsatisfactory characteristics of currently available affinity membranes and the need for further improvements in the art.